Recently, a digital television service using a wired and wireless communication network has been generalized. The digital TV service may provide various services that could not be provided in an existing analog broadcasting service.
For example, an internet protocol television (IPTV) service, which is a kind of digital TV services, provides bi-directionality allowing a user to actively select a kind of viewing programs, a viewing time thereof, or the like. The IPTV service may also provide various services, such as the Internet search, a home shopping, an online game, and the like, based on this bi-directionality.